clipka <ano### [at] anonymousorg> wrote:
> Am 19.10.2016 um 07:13 schrieb omniverse:
>
> > Seeing this I began trying to find out if the File_Gamma=srgb I just began using
> > recently was making a difference from File_Gamma=2.2 I had been using prior to
> > that.
> >
> > Well, that wasn't the thing that caused me a tremendous surprise because I was
> > only seeing a real change if using assumed_gamma=1 for global_settings instead
> > of srgb I also started using for that. A brightened image, as expected, which is
> > why I had trouble with the idea of the necessity of adding it to all my scene
> > files the many years ago now.
>
> This is to be expected /if/ you were using PNG output.
>
> Most image file formats require that the generating software encodes the
> image data to match the viewing system's gamma. This is what is known as
> "gamma pre-correction". If the generating software encodes for a
> different gamma, the viewing system will display the image differently.
>
> The PNG file format, on the other hand, allows the generating software
> to choose an encoding gamma independently, and store the chosen gamma in
> the file header; it is then up to the viewing system to read that gamma
> information, and decode the data accordingly. Provided the decoding
> software supports this mode of operation, it can therefore properly
> display the image data in the same manner no matter the encoding gamma.
>
>
> > By using Antialias_Gamma=1 in my povray.ini the rendering I was testing all this
> > with went from over a minute (plus 3 to 10 seconds) to only 20 seconds!!!
> >
> > I put 2 of those images together or overlayed, one with and one without that
> > option, applied as differences between them and it didn't show anything. No
> > differences visible.
> >
> > So I must ask, is that to be expected?
>
> I'm a bit surprised about the magnitude, but I consider it possible, as
> changing "Antialias_Gamma" also changes the effective anti-aliasing
> threshold, though the effect also depends on the absolute brightness of
> the colours.
>
> However, with the symptoms observed you should be able to get about the
> same speedup in render times by choosing a higher anti-aliasing
> threshold, also without loss of quality.

Hadn't thought about the file format being a factor I always used PNG though,
sometimes JPG.

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